Search

Multisensory sensitivity (MSS), observed in some chronic pain patients, may reflect a generalized central nervous system sensitivity. While several surveys measure aspects of MSS, there remains no gold standard. We explored the underlying constructs of four MSS-related surveys (80 items in total) using factor analyses using REDCap surveys (N = 614, 58.7% with pain). Four core- and six associated-MSS factors were identified from the items assessed. None of these surveys addressed all major sensory systems and most included additional related constructs. A revised version of the Somatosensory Amplification Scale was developed, encompassing five core MSS systems: vision, hearing, smell, tactile, and internal bodily sensations: the 12-item Multisensory Amplification Scale (MSAS). The MSAS demonstrated good internal consistency (alpha = 0.82), test-retest reliability (ICC3,1 = 0.90), and construct validity in the original and in a new, separate cohort (R = 0.54 - 0.79, p < 0.0001). Further, the odds of having pain were 2 - 3.5 times higher in the highest sex-specific MSAS quartile relative to the lowest MSAS quartile, after adjusting for age, sex, BMI, and pain schema (p < 0.03). The MSAS provides a psychometrically comprehensive, brief, and promising tool for measuring the core-dimensions of MSS. PERSPECTIVE: Multiple multisensory sensitivity (MSS) tools are used, but without exploration of their underlying domains. We found several measures lacking core MSS domains, thus we modified an existing scale to encompass five core MSS domains: light, smell, sound, tactile, and internal bodily sensations using only 12 items, with good psychometric properties.

OBJECTIVE: Adults with radiographic knee OA (rKOA) are at increased risk of mortality and walking difficulty may modify this relation. Little is known about specific aspects of walking difficulty that increase mortality risk. We investigated the association of walking speed (objective measure of walking difficulty) with mortality and examined the threshold that best discriminated this risk in adults with rKOA. METHODS: Participants with rKOA from the Johnston County Osteoarthritis Project (JoCoOA, longitudinal population-based cohort), Osteoarthritis Initiative and Multicenter Osteoarthritis Study (OAI and MOST, cohorts of individuals with or at high risk of knee OA) were included. Baseline speed was measured via 2.4-meter (m) walk test (short-distance) in JoCoOA and 20-m walk test (standard-distance) in OAI and MOST. To examine the association of walking speed with mortality risk over nine years, hazard ratios (aHR) and 95% confidence intervals (CI) were calculated from Cox regression models adjusted for potential confounders., A Maximal Likelihood Ratio Chi-square Approach was utilized to identify an optimal threshold of walking speed predictive of mortality. RESULTS: Deaths after 9 years of follow-up occurred in 23.3% (290/1244) of JoCoOA and 5.9% (249/4215) of OAI+MOST. Walking 0.2 meters/second slower during short- and standard-distance walk tests was associated with 23% (aHR[95%CI]; 1.23[1.10, 1.39]) and 25% (1.25[1.09, 1.43]) higher mortality risk, respectively. Walking

Purpose Some individuals with chronic pain find daily life sensations (eg, noise, light, or touch) aversive. This amplification of multisensory sensations has been associated with centrally mediated plasticity; for example, greater multisensory sensitivity (MSS) occurs in patients with fibromyalgia than rheumatoid arthritis. However, whether MSS preferentially relates to pain measures which reflect central influences (eg, dynamic quantitative sensory testing (QST) or referred pain), or whether the MSS-pain relationship requires priming from chronic pain, is unknown. Thus, this cross-sectional study investigated the relationships between MSS assessed in a pain-free state and evoked pain sensitivity. Methods Experimental intramuscular infusion pain and multiple static and dynamic QST were assessed in 465 healthy, pain-free adults: pain thresholds using pressure (PPTs) and heat (HPTs), temporal summation of pain (TSP) using pressure, heat or punctate stimuli, and conditioned pain modulation (CPM) using pressure or heat test stimuli. MSS was assessed using 7 items from Barsky's Somatosensory Amplification Scale. Differences in pain and QST between sex-specific MSS quartiles were assessed, adjusting for multiple comparisons. All participants completed at least one intramuscular infusion condition, but not all were asked to complete each QST (n=166-465). Results Both static and dynamic QST differed between highest and lowest MSS quartiles using pressure stimuli: lower PPTs (adjusted-p 0.05). Odds of experiencing TSP or referred pain was not greater, whereas CPM was 8-fold less likely, in those with highest MSS. Conclusion Normal variation in non-noxious MSS is related to both static and dynamic pain sensitivity, without sensitization associated with chronic pain, but is dependent on the QST stimulus. Thus, common influences on MSS and pain sensitivity may involve central mechanisms but are likely more complex than previously recognized.

Study Design Clinical commentary. Introduction/Purpose Pain and movement are universally relevant phenomena that influence human experiences in readily observable ways. Improved understanding of pain-movement relationships can guide medical and rehabilitative approaches to recovery and decrease risk of dysfunctional long-term consequences of otherwise normal neuromuscular responses. Therefore, the overall intent of this article is to elucidate the relationships between pain and movement as they relate to clinical decision making. Conclusions Motor output is highly adaptable, can be influenced by multiple mechanisms at various levels along the nervous system, and may vary between individuals despite similar diagnoses. Therefore, interventions need to be individualized and consider both the types of motor response observed (ie, whether the response is protective or maladaptive), and the patient's acute physical activity tolerance when prescribing exercise/movement.

Wrist-worn accelerometers are increasingly used to assess free-living physical activity (PA), but the implications of different processing methods are not well characterized. To advance research in this area it is important to better understand how choice of processing method influences estimates of free-living PA behavior. This study compared PA profiles resulting from processing wrist-worn data collected under free-living conditions using four different methods in a clinical sample of 160 women with chronic pain, a condition for which PA serves as a treatment. Participants wore monitors on their non-dominant wrist for 7 days and completed a self-report PA measure. Processing methods were Hildebrand linear, a modified nonlinear Hildebrand, Staudenmayer linear, and Staudenmayer random forest. Using each method, minutes per day in sedentary, light, and moderate-to-vigorous PA (MVPA) were estimated and individuals were classified as meeting PA guidelines based on their accumulated MVPA. Comparisons of outcomes among processing methods and with self-reported PA were made using repeated measures ANOVA, correlations, and kappa statistics. With few exceptions, estimated time at each intensity differed significantly across processing methods and with self-report (p range = 0.09 to 1.00) and showed inconsistent agreement for classifying individuals as meeting PA guidelines (κrange: −0.02 to 0.90). Thus, choice of processing method significantly influenced conclusions regarding free-living PA. Researchers and clinicians should exercise caution when interpreting accelerometer activity data and comparing across existing studies using different processing methods when examining how PA influences clinical conditions.

INTRODUCTION: We have a limited understanding of how antagonist muscle coactivation relates to measurement of strength in both individuals with and without knee osteoarthritis (KOA). OBJECTIVE: We sought to determine if hamstring coactivation during a maximal quadriceps activation task attenuates net quadriceps strength. DESIGN: Cross-sectional cohort analysis was conducted using data from the 60-month visit of the Multicenter Osteoarthritis Study (MOST). SETTING: Laboratory PARTICIPANTS: A sample of 2328 community-dwelling MOST participants between the ages of 55 and 84 years, with or at elevated risk for KOA, completed the 60-month MOST follow-up visit. Of these, 1666 met inclusion criteria for the current study. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURE(S): Quadriceps strength; percent combined hamstring coactivation (HC), medial HC, and lateral HC. Quadriceps and hamstring strength were assessed using an isokinetic dynamometer. Surface electromyography was used to assess muscle activation patterns. General linear models, adjusted for age, BMI, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Kellgren-Lawrence (KL) grade and study site, modeled the relationship between antagonist hamstring coactivation and quadriceps strength. RESULTS: Men had significantly greater quadriceps strength (p

Objective: The objective of the review is to determine whether conditioned pain modulation (CPM) is impaired in adults with chronic low back pain (CLBP) when compared with pain-free individuals. Methods: A a systematic search of the literature was undertaken using the databases: MEDLINE, Scopus, CINAHL and Web of Science. The citations of included studies were reviewed for additional studies. Observational, cross-sectional, case-control studies published in English between January 1990 and August 2019 were considered. Studies that investigated the efficiency of standardized CPM regimens among defined cases of CLBP and in comparison, with pain-free controls were included. After initial title and abstract screening, 2 authors reviewed the full texts of the eligible articles independently. Risk of bias was carried out using assessment of 4 categories: blinding of the outcome assessors, representativeness of cases to the specified population, comparability of cases and controls, and control of confounding variables. Results: In total, 643 records were identified, of which 7 studies were included. Overall, the results of the studies reported mixed conclusions on the efficiency of CPM in CLBP. Three studies identified significant differences for CPM between CLBP and pain-free controls and the other 4 studies reported no significant differences. The common methodological limitations were unclear reporting about blinding of the outcome assessors and inadequate control of confounding factors. Conclusions: High-quality research is strongly recommended to determine the function of endogenous pain modulatory mechanisms in CLBP.

Objectives: To examine whether physical activity (PA) was associated with fatigue, and quantify the extent of potential mediation through depressive symptoms or physical function (PF) on the relationship between PA and fatigue in symptomatic knee osteoarthritis (KOA).Method: This longitudinal study used data from the Multicenter Osteoarthritis Study (n=484), comprising subjects aged ≥50years. Baseline PA was quantified via an ankle-worn accelerometer. The outcome was fatigue, measured using a 0-10 rating scale at 2 year follow-up. Mediators included gait speed as a measure of PF and depressive symptoms at 2 year follow-up. Mediation analysis was carried out after adjustment for baseline confounders. Stratified analysis by baseline fatigue status [no/low (

Summary Objective To examine the relation of pain sensitization to altered motor activity in knee OA as assessed by hamstrings muscle co-contraction during maximal effort knee extension. Design Medial, lateral, and overall hamstring co-contraction was assessed in the Multicenter Osteoarthritis (MOST) Study cohort using electromyography during isokinetic knee extension at 60°/second. Mechanical temporal summation of pain (TS) was assessed at the right wrist and pressure pain thresholds (PPT) were assessed at the patellae; PPTs were categorized into sex-specific tertiles. Muscle co-contraction was categorized into age- and sex-specific tertiles. We evaluated the relation of measures of sensitization to muscle co-contraction using a generalized logistic regression model. Results 1633 participants were included: mean age and BMI was 67.3 ± 7.7 years and 30.3 ± 5.6 kg/m2, respectively; 58% were female. Presence of TS was associated with higher overall (OR 1.3, 95% confidence interval (CI) (1.0–1.8)), medial (1.4 (1.0–1.9), and lateral (1.3 (1.0, 1.9)) hamstring co-contraction. The lowest PPT tertile (greater sensitivity) was associated with higher overall (1.5 (1.0, 2.3)) and medial (1.5 (1.0, 2.3)) hamstring co-contraction compared with those in the highest PPT tertile. Conclusion Greater pain sensitization, as assessed by presence of TS at the wrist and low patellar PPT, was associated with greater overall and medial hamstring co-contraction during knee extension. This provides support to the possibility that peripheral and/or central nervous system alterations may not only affect pain sensitivity, but also motor function.

An acute bout of physical activity and exercise can increase pain in individuals with chronic pain, but regular exercise is an effective treatment. This review will discuss these two dichotomous findings by summarizing studies in human and animal subjects. We will provide the data that supports the role of physical activity in modulating central nervous system excitability and inhibition, immune system function, and psychological constructs associated with pain. We show evidence that the sedentary condition is associated with greater excitability and less inhibition in both the central nervous system (brainstem inhibitory/facilitatory sites) and the immune system. We further show that exercise and regular physical activity decreases excitability and improves inhibition in both the central nervous system (brainstem inhibitory/facilitatory sites) and the immune system. We will then discuss the clinical implications of these findings, make recommendations for clinical application of exercise, and suggest future research directions.

Quantifying pain intensity using a numerical rating scale is a well validated means for assessing the subjective perception of pain. A cognitive framework to interpret and characterize a concept is referred to as a schema. The schema used to conceptualize pain rating can vary, potentially through assimilation of new experiences and information. Thus, whether pain-rating schema differ systematically between those with chronic pain and pain-free individuals is unknown. Secondary analysis of a survey dataset were used to compare pain rating schema across individuals with various forms of chronic pain (n= 785) and pain-free adults (n=451). Schema were assessed using 6 items from the Pain Severity Questionnaire (Frey Law, et al 2014), as part of a larger study. Mean ratings (0 – 10 scale, allowing 0.5 intervals) for 2 common hypothetical pain conditions: mild, moderate, and severe headache and joint pain. Differences and percent reduction between severities were assessed between subgroups, based on type nad number of pain co-morbidities. Patients with FM, with or without multiple pain co-morbidities reported higher pain ratings than pain-free individuals across mild, moderate and severe conditions by approximately 1 out of 10 (p

We have shown people with fibromyalgia experience exacerbated pain in the exercising limb up to three days following submaximal isometric and concentric exercise however, the pain response following eccentric exercise has not been investigated. This study investigated the change in experimental pain up to two days following submaximal eccentric exercise while clinical pain was assessed through the 7-day recovery period in women with and without FM. Eighteen women with fibromyalgia (49.1±11.8yr, BMI: 31.4±7.6) and 18 controls (49.5±10.1yr, BMI: 27.1±4.8) completed session 1 (exercise) and session 2 (recovery assessment) separated by 2 days; session 1 included a 10-minute bout of submaximal (20% of maximal voluntary contraction) eccentric exercise with the right elbow flexors. Pressure pain thresholds (PPTs), mechanical pain summation, and punctate pain summation were assessed before, immediately after exercise, and in session 2. Clinical pain (0-10 NRS) in the exercising arm and whole-body was assessed before, during, immediately after, and up to seven days following the exercise bout. PPTs and mechanical pain summation did not change immediately following exercise or session 2 (Time, p>0.05). Punctate pain summation changed following exercise (Time x Summation, p=0.003) however, post hoc analysis did not reveal a significant difference immediately after exercise (p=0.296) or at session two (p=0.03). The fibromyalgia group reported greater increases in exercising arm pain during (Time x Group, p

Background The ankle is an important component of the human kinetic chain, and deficits in ankle strength can negatively impact functional tasks such as balance and gait. While peak torque is influenced by joint angle and movement velocity, ankle strength is typically reported for a single angle or movement speed. To better identify deficits and track recovery of ankle strength after injury or surgical intervention, ankle strength across a range of movement velocities and joint angles in healthy adults is needed. Thus, the primary goals of this study were to generate a database of strength values and 3-dimensional strength surface models for plantarflexion (PF) and dorsiflexion (DF) ankle strength in healthy men and women. Secondary goals were to develop a means to estimate ankle strength percentiles as well as examine predictors of maximal ankle strength in healthy adults. Methods Using an isokinetic dynamometer, we tested PF and DF peak torques at five joint angles (−10° [DF], 0° [neutral], 10° [PF], 20° [PF] and 30° [PF]) and six velocities (0°/s, 30°/s, 60°/s, 90°/s, 120°/s and 180°/s) in 53 healthy adults. These data were used to generate 3D plots, or “strength surfaces”, for males and females for each direction; surfaces were fit using a logistic equation. We also tested predictors of ankle strength, including height, weight, sex, and self-reported physical activity levels. Results Torque-velocity and torque-angle relationships at the ankle interact, indicating that these relationships are interdependent and best modeled using 3D surfaces. Sex was the strongest predictor of ankle strength over height, weight, and self-reported physical activity levels. 79 to 97 % of the variance in mean peak torque was explained by joint angle and movement velocity using logistic equations, for men and women and PF and DF directions separately. Conclusions The 3D strength data and surface models provide a more comprehensive dataset of ankle strength in healthy adults than previously reported. These models may allow researchers and clinicians to quantify ankle strength deficits and track recovery in patient populations, using angle- and velocity-specific ankle strength values and/or strength percentiles from healthy adults. Electronic supplementary material The online version of this article (doi:10.1186/s13047-016-0174-1) contains supplementary material, which is available to authorized users.

Objective It is not clear why some individuals develop pain with knee osteoarthritis (OA). We undertook this study to identify pain susceptibility phenotypes (PSPs) and their relationship to incident persistent knee pain (PKP) 2 years later. Methods We identified individuals free of PKP from the Multicenter Osteoarthritis Study, a longitudinal cohort of older adults with or at risk of knee OA. Latent class analysis was used to determine PSPs that may contribute to development of PKP apart from structural pathology. These included widespread pain, poor sleep, and psychological factors as well as pressure pain threshold and temporal summation (TS) as determined by quantitative sensory testing (QST). We used logistic regression to evaluate the association of sociodemographic factors with PSPs and the relationship of PSPs to the development of PKP over 2 years. Results A total of 852 participants were included (mean age 67 years, body mass index 29.5 kg/m2 , 55% women). Four PSPs were identified, primarily characterized by varying proportions (low/absent, moderate, or high) of the presence of pressure pain sensitivity and of facilitated TS, reflecting different measures of sensitization. Subjects in the PSP with a high proportion of pressure pain sensitivity and a moderate proportion of facilitated TS were twice as likely to develop incident PKP over 2 years (odds ratio 1.98 [95% confidence interval 1.07-3.68]) compared with subjects in the PSP having a low proportion of sensitization by both measures. Conclusion Four PSPs were identified, 3 of which were predominated by QST evidence of sensitization and 1 of which was associated with developing PKP 2 years later. Prevention or amelioration of sensitization may be a novel approach to preventing onset of PKP in OA.

Although the rotator cuff muscles are susceptible to fatigue, shoulder fatigue studies reporting torque decline during intermittent tasks are relatively uncommon in the literature. A previous modification to the three-compartment controller (3CC) fatigue model incorporated a rest recovery multiplier (3CC-r model) to represent augmented blood flow to muscle during rest intervals ( Looft et al., 2018 ). A rest recovery value of r = 15 was optimal for ankle, knee, and elbow joint regions, whereas r = 30 was better for hand/grip muscles. However, shoulder torque decline data was unavailable in the literature for comparison. Thus, the purpose of this study was to collect fatigue data for two different intermittent, isometric shoulder flexion fatiguing tasks and assess the 3CC-r model with r = 15 or 30 compared to the original 3CC model. Twenty healthy participants (9 M) completed two fatigue tasks: 50% maximum voluntary contraction (MVC) with 50% duty cycle (DC) and 70% MVC with 70% DC. MVCs were assessed at discrete time points (1, 3, 5, 10, and 15 min) until endurance time (MET). Mean observed percent torque decline (%TD) for the two tasks were compared to three model estimates: 3CC-r (using r = 15 and r = 30) and 3CC. Using these data, we confirmed that the addition of a rest multiplier (r = 15 somewhat better than r = 30) substantially improved predictions of shoulder fatigue using a previously validated analytical fatigue model (3CC). The relatively large reduction in model errors over the original model suggests the importance of representing augmented recovery during rest periods.

Pain reduction is a primary goal of physical therapy for patients who present with acute or persistent pain conditions. The purpose of this review is to describe a mechanism-based approach to physical therapy pain management. It is increasingly clear that patients need to be evaluated for changes in peripheral tissues and nociceptors, neuropathic pain signs and symptoms, reduced central inhibition and enhanced central excitability, psychosocial factors, and alterations of the movement system. In this Perspective, 5 categories of pain mechanisms (nociceptive, central, neuropathic, psychosocial, and movement system) are defined, and principles on how to evaluate signs and symptoms for each mechanism are provided. In addition, the underlying mechanisms targeted by common physical therapist treatments and how they affect each of the 5 categories are described. Several different mechanisms can simultaneously contribute to a patient's pain; alternatively, 1 or 2 primary mechanisms may cause a patient's pain. Further, within a single pain mechanism, there are likely many possible subgroups. For example, reduced central inhibition does not necessarily correlate with enhanced central excitability. To individualize care, common physical therapist interventions, such as education, exercise, manual therapy, and transcutaneous electrical nerve stimulation, can be used to target specific pain mechanisms. Although the evidence elucidating these pain mechanisms will continue to evolve, the approach outlined here provides a conceptual framework for applying new knowledge as advances are made.

Background Although exercise is an effective treatment for fibromyalgia, the relationships between lifestyle physical activity and multiple symptomology domains of fibromyalgia are not clear. Thus, the purpose of this study was to comprehensively examine the relationships between lifestyle physical activity with multiple outcome domains in women with fibromyalgia, including pain, fatigue, function, pain-related psychological constructs, and quality of life. Methods Women (N = 171), aged 20 to 70 years, diagnosed with fibromyalgia, recruited from an ongoing two-site clinical trial were included in this prespecified subgroup analysis of baseline data. Physical activity was assessed using self-report and accelerometry. Symptomology was assessed using questionnaires of perceived physical function, quality of life, fatigue, pain intensity and interference, disease impact, pain catastrophizing, and fear of movement. In addition, quantitative sensory testing of pain sensitivity and performance-based physical function were assessed. Correlation coefficients, regression analyses and between-group differences in symptomology by activity level were assessed, controlling for age and body mass index (BMI). Results Lifestyle physical activity was most closely associated with select measures of physical function and fatigue, regardless of age and BMI. Those who performed the lowest levels of lifestyle physical activity had poorer functional outcomes and greater fatigue than those with higher physical activity participation. No relationships between lifestyle physical activity and pain, pain sensitivity, or pain-related psychological constructs were observed. Conclusions Lifestyle physical activity is not equally related to all aspects of fibromyalgia symptomology. Lifestyle physical activity levels have the strongest correlations with function, physical quality of life, and movement fatigue in women with fibromyalgia. No relationships between lifestyle physical activity and pain, pain sensitivity, or psychological constructs were observed. These data suggest that physical activity levels are more likely to affect function and fatigue, but have negligible relationships with pain and pain-related psychological constructs, in women with fibromyalgia. Trial registration ClinicalTrials.gov, NCT01888640. Registered on 28 June 2013. Electronic supplementary material The online version of this article (10.1186/s13075-018-1671-3) contains supplementary material, which is available to authorized users.

Objective.Whether widespread pain (WSP) affects the risk of developing knee pain or knee osteoarthritis (OA) is unknown and could enhance understanding of pain mechanisms in OA.Methods.Subjects from the Multicenter OA (MOST) study, a US National Institutes of Health–funded prospective cohort of older adults with or at risk of knee OA, were characterized regarding WSP, defined as pain above and below the waist on both sides of the body and axially using a standard homunculus, excluding knee pain at 60 months (baseline). Followup occurred 2 years later. We assessed the relation of WSP to odds of knee pain worsening (≥ 2-point increase in the Western Ontario and McMaster Universities Arthritis Index pain subscale) using logistic regression, and to odds of incident radiographic knee OA (ROA; Kellgren-Lawrence arthritis scale ≥ grade 2 of either knee among those free of ROA at baseline) and incident consistent frequent knee pain (CFKP; knee pain on most days during the past month among participants free of knee pain at baseline) in 1 or both knees using multinomial regression adjusting for potential confounders.Results.There were 1752 participants available for analysis [mean age (SD) 67.0 yrs (7.7), body mass index 30.5 kg/m2(5.9), 59% women]. Baseline presence of WSP was not associated with worsened knee pain (adjusted OR 1.15, 95% CI 0.89–1.48, p = 0.30), ROA (adjusted OR 0.86, 95% CI 0.46–1.63, p = 0.65), or incident CFKP (adjusted OR 1.69, 95% CI 0.96–2.96, p = 0.07).Conclusion.WSP was not significantly associated with worsening knee pain, incident ROA, or CFKP. Development of knee pain and ROA does not appear to be influenced by underlying WSP.

Chronic muscle pain affects 20-50% of the population, is more common in women than men, and is associated with increased pain during physical activity and exercise. Muscle fatigue is common in people with chronic muscle pain, occurs in response to exercise, and is associated with release of fatigue metabolites. Fatigue metabolites can sensitize muscle nociceptors, which could enhance pain with exercise. Using a mouse model we tested whether fatigue of a single muscle, induced by electrical stimulation, resulted in enhanced muscle hyperalgesia and if the enhanced hyperalgesia was more pronounced in female mice. Muscle fatigue was induced in combination with a sub-threshold muscle insult (2 injections of pH 5.0 saline) in male and female mice. We show that male and female mice, fatigued immediately prior to muscle insult in the same muscle, develop similar muscle hyperalgesia 24 hours later. However, female mice also develop hyperalgesia when muscle fatigue and muscle insult occur in different muscles, and when muscle insult is administered 24 hours after fatigue in the same muscle. Further, hyperalgesia lasts significantly longer in females. Finally, muscle insult with or without muscle fatigue results in minimal inflammatory changes in the muscle itself, and sex differences are not related to estradiol (ovariectomy) or changes in brainstem activity (pNR1). Thus, the current model mimics muscle fatigue-induced enhancement of pain observed in chronic muscle pain conditions in the human population. Interactions between fatigue and muscle insult may underlie the development of chronic widespread pain with an associated female predominance observed in human subjects.

BackgroundParticipation is an important, yet seldom studied, outcome after total knee replacement (TKR).ObjectiveThe purpose of this study was to investigate the extent and predictors of participation and participation restriction among people after TKR.Materials and MethodsThis study investigated the changes in pain, function, and participation scores (measured using a subscale of the Late-Life Function and Disability Instrument) from pre-TKR to ≥1 year post-TKR among a subsample of participants from the Multicenter Osteoarthritis Study (MOST) longitudinal cohort (MOST is funded by the National Institutes of Health). The proportions of individuals with participation restriction pre-TKR and ≥1 and ≥2 years post-TKR were calculated for all participants and for important demographic subgroups. The association between demographic and clinical factors and participation was estimated using linear regression. The association between demographic and clinical factors and participation restriction was estimated using logistic regression.ResultsThere were 292 individuals with outcome data ≥1 year post-TKR. Of these, 218 (75%) had data pre-TKR and ≥1 year post-TKR and 160 (55%) had data ≥2 years post-TKR. There were mean improvements in pain, function, and participation at ≥1 and 2 years. However, approximately 30% of the study sample had participation restriction pre-TKR and post-TKR, and the proportion decreased significantly only for those LimitationsThe time between pre-TKR and post-TKR assessment varied across study participants, and data were not available on their rehabilitation utilization.ConclusionsAlthough there was a mean increase in participation ≥1 year following TKR, participation restriction was common. The likelihood of low participation was increased among women, non-whites, and those with depressive symptoms, severe pain in either knee, or worse pre-TKR function.

Background: Recent studies suggest an underlying three- or four-factor structure explains the conceptual overlap and distinctiveness of several negative emotionality and pain-related constructs. However, the validity of these latent factors for predicting pain has not been examined. Methods: A cohort of 189 (99 female, 90 male) healthy volunteers completed eight self-report negative emotionality and pain-related measures (Eysenck Personality Questionnaire – Revised, Positive and Negative Affect Schedule, State-Trait Anxiety Inventory, Pain Catastrophizing Scale, Fear of Pain Questionnaire; Somatosensory Amplification Scale, Anxiety Sensitivity Index and Whiteley Index). Using principal axis factoring, three primary latent factors were extracted: general distress, catastrophic thinking and pain-related fear. Using these factors, individuals clustered into three subgroups of high, moderate and low negative emotionality responses. Experimental pain was induced via intramuscular acidic infusion into the anterior tibialis muscle, producing local (infusion site) and/or referred (anterior ankle) pain and hyperalgesia. Results: Pain outcomes differed between clusters (multivariate analysis of variance and multinomial regression), with individuals in the highest negative emotionality cluster reporting the greatest local pain (p = 0.05), mechanical hyperalgesia (pressure pain thresholds; p = 0.009) and greater odds (2.21 odds ratio) of experiencing referred pain when compared to the lowest negative emotionality cluster. Conclusion: Our results provide support for three latent psychological factors explaining the majority of the variance between several pain-related psychological measures, and that individuals in the high negative emotionality subgroup are at increased risk for (1) acute local muscle pain; (2) local hyperalgesia; and (3) referred pain using a standardized nociceptive input.

The development of patient profiles to subgroup individuals on a variety of variables has gained attention as a potential means to better inform clinical decision making. Patterns of pain sensitivity response specific to quantitative sensory testing (QST) modality have been demonstrated in healthy subjects. It has not been determined whether these patterns persist in a knee osteoarthritis population. In a sample of 218 participants, 19 QST measures along with pain, psychological factors, self-reported function, and quality of life were assessed before total knee arthroplasty. Component analysis was used to identify commonalities across the 19 QST assessments to produce standardized pain sensitivity factors. Cluster analysis then grouped individuals who exhibited similar patterns of standardized pain sensitivity component scores. The QST resulted in 4 pain sensitivity components: heat, punctate, temporal summation, and pressure. Cluster analysis resulted in 5 pain sensitivity profiles: a "low pressure pain" group, an "average pain" group, and 3 "high pain" sensitivity groups who were sensitive to different modalities (punctate, heat, and temporal summation). Pain and function differed between pain sensitivity profiles, along with sex distribution; however, no differences in osteoarthritis grade, medication use, or psychological traits were found. Residualizing QST data by age and sex resulted in similar components and pain sensitivity profiles. Furthermore, these profiles are surprisingly similar to those reported in healthy populations, which suggests that individual differences in pain sensitivity are a robust finding even in an older population with significant disease.

The development of localized muscle fatigue has classically been described by the nonlinear intensity-endurance time (ET) curve (Rohmert, 1960; El Ahrache et al., 2006). These empirical intensity-ET relationships have been well-documented and vary between joint regions. We previously proposed a three-compartment biophysical fatigue model, consisting of compartments (i.e. states) for active (M(A)), fatigued (M(F)), and resting (M(R)) muscles, to predict the decay and recovery of muscle force (Xia and Frey Law, 2008). The purpose of this investigation was to determine optimal model parameter values, fatigue (F) and recovery (R), which define the "flow rate" between muscle states and to evaluate the model's accuracy for estimating expected intensity-ET curves. Using a grid-search approach with modified Monte Carlo simulations, over 1 million F and R permutations were used to predict the maximum ET for sustained isometric tasks at 9 intensities ranging from 10% to 90% of maximum in 10% increments (over 9 million simulations total). Optimal F and R values ranged from 0.00589 (F(ankle)) and 0.0182 (R(ankle)) to 0.00058 (F(shoulder)) and 0.00168 (R(shoulder)), reproducing the intensity-ET curves with low mean RMS errors: shoulder (2.7s), hand/grip (5.6s), knee (6.7s), trunk (9.3s), elbow (9.9s), and ankle (11.2s). Testing the model at different task intensities (15-95% maximum in 10% increments) produced slightly higher errors, but largely within the 95% prediction intervals expected for the intensity-ET curves. We conclude that this three-compartment fatigue model can be used to accurately represent joint-specific intensity-ET curves, which may be useful for ergonomic analyses and/or digital human modeling applications.

The sulcus angle has been widely used in the literature as a measure of trochlear morphology. Recently, lateral trochlear inclination and trochlear angle have been reported as alternatives. The purpose of this study was to determine the association between measures of trochlear morphology and patellofemoral joint (PFJ) cartilage damage and bone marrow lesions (BMLs). 907 knees were selected from the Multicenter Osteoarthritis Study, a cohort study of persons aged 50-79 years with or at risk for knee OA. Trochlear morphology was measured using lateral trochlear inclination, trochlear angle, and sulcus angle on axial MRI images; cartilage damage and BMLs were graded on MRI. We determined the association between quartiles of each trochlear morphology level with the presence or absence of cartilage damage and BMLs in the PFJ using logistic regression. The strongest associations were seen with lateral trochlear inclination and lateral PFJ cartilage damage and BMLs, with knees in the lowest quartile (flattened lateral trochlea) having more than two times the odds of lateral cartilage damage and BMLs compared to those in the highest quartile (p

It is not clear whether heightened pain sensitivity in knee osteoarthritis (OA) is related to sensitisation induced by nociceptive input from OA pathology ('state') versus other confounding factors. Conversely, some individuals may be predisposed to sensitisation irrespective of OA ('trait').The Multicenter Osteoarthritis Study is a longitudinal cohort of persons with or at risk of knee OA. We obtained knee X-rays, pain questionnaires and comprehensive assessment of factors that can influence pain sensitivity. We examined the relation of sensitisation and sensitivity assessed by mechanical temporal summation (TS) and pressure pain thresholds (PPTs) to knee OA and knee pain severity. To test whether sensitisation and sensitivity is a 'state' induced by OA pathology, we examined the relation of PPT and TS to knee OA duration and severity.In 2126 subjects (mean age 68, mean body mass index (BMI) 31, 61% female), PPT and TS were not associated with radiographic OA (ORs 0.9-1.0 for PPT and TS; p0.05). However, PPT and TS were associated with pain severity (ORs: 1.7-2.0 for PPT; 1.3-1.6 for TS; p0.05). Knee OA duration and radiographic severity were not associated with PPT or TS.PPT and TS were associated with OA-related pain, but not radiographic OA after accounting for pertinent confounders in this large cohort. Lack of association with disease duration suggests at least some sensitisation and pain sensitivity may be a trait rather than state. Understanding the relationship between pathological pain and pain sensitivity/sensitisation offers insight into OA pain risk factors and pain management opportunities.

ObjectiveTo determine whether women experience greater knee pain severity than men at equivalent levels of radiographic knee osteoarthritis (OA).Design and methodsA cross-sectional analysis of 2712 individuals (60% women) without knee replacement or a recent steroid injection. Sex differences in pain severity at each Kellgren-Lawrence (KL) grade were assessed by knee using visual analog scale (VAS) scale and Western Ontario and McMaster Universities Arthritis Index (WOMAC) with and without adjustment for age, analgesic use, Body mass index (BMI), clinic site, comorbid conditions, depression score, education, race, and widespread pain (WSP) using generalized estimating equations. Effect sizes (Cohen's d) were also calculated. Analyses were repeated in those with and without patellofemoral OA (PFOA).ResultsWomen reported higher VAS pain at all KL grades in unadjusted analyses (d=0.21-0.31, P&nbsp

Laura A Frey-Law,1 Jennifer E Lee,2,3 Alex M Wittry,4 Myles Melyon5 1Department of Physical Therapy and Rehabilitation Science, The University of Iowa, Iowa City, IA, USA; 2Mount Mercy University, Department of Psychology, Cedar Rapids, IA, USA; ³College of Nursing, The University of Iowa, 4Department of Emergency Medicine, The University of Iowa Hospitals and Clinics, Iowa City, IA, USA; 5Midwestern University, Glendale, AZ, USA Background: While the validity of pain assessment has been well documented, the underlying schema (ie, organized, preconceived ideas) of how individuals interpret numerical pain ratings is not well understood. This study's objectives were to examine numerical pain intensity ratings, from (0 to 10 cm on the visual analog scale [VAS]) across multiple severities of commonly experienced acute pain conditions to determine whether the ratings differed between these pain conditions and/or between individuals. Methods: A community sample (N=365, 66% female) rated their anticipated pain intensity (VAS) for threshold, mild, moderate, severe, and tolerance level, using several common pain conditions: headache, toothache, joint injury, delayed-onset muscle soreness, burns, and “general pain.” Results: Cluster analysis revealed three subgroups of individuals, suggesting three types of underlying pain rating schema: 1) Low Rating subgroup (low VAS pain intensity ratings across all the pain severity categories); 2) Low/High Rating subgroup (low VAS pain intensity rating for mild, but high VAS pain intensity rating for severe pain); and 3) High Rating subgroup (high VAS pain intensity ratings across all the pain severity categories). Overall, differences between pain conditions were small: muscle soreness pain intensity was consistently rated lower than the other pain types across severities. The highest pain ratings varied between joint injury and general pain, depending on severity level. No effects of sex or current experience of pain were noted. Conclusion: The results indicate that: 1) three distinct pain schemas were present in this community-based sample, indicating significant variation in how pain scales are utilized and/or interpreted between clusters of individuals; 2) pain ratings vary by condition, but these differences are minor; and 3) pain rating schemas are not significantly different between males and females or between individuals with and without current pain. Keywords: VAS, muscle soreness, headache, toothache, joint pain

Objective.Poor functional outcomes post–knee replacement are common, but estimates of its prevalence vary, likely in part because of differences in methods used to assess function. The agreement between improvement in function and absolute good levels of function after knee replacement has not been evaluated. We evaluated the attainment of improvement in function and absolute good function after total knee replacement (TKR) and the agreement between these measures.Methods.Using data from The Multicenter Osteoarthritis (MOST) Study, we determined the prevalence of achieving a minimal clinically important improvement (MCII, ≥ 14.2/68 point improvement) and Patient Acceptable Symptom State (PASS, ≤ 22/68 post-TKR score) on the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) Physical Function subscale at least 6 months after knee replacement. We also assessed the frequency of co-occurrence of the 2 outcomes, and the prevalence according to pre-knee replacement functional status.Results.We included 228 subjects who had a knee replacement during followup (mean age 65 yrs, mean body mass index 33.4, 73% female). Seventy-one percent attained the PASS for function after knee replacement, while only 44% attained the MCII. Of the subjects who met the MCII, 93% also attained the PASS; however, of subjects who did not meet the MCII, 54% still achieved a PASS. Baseline functional status was associated with attainment of each MCII and PASS.Conclusion.There was only partial overlap between attainment of a good level of function and actually improving by an acceptable amount. Subjects were more likely to attain an acceptable level of function than to achieve a clinically important amount of improvement post–knee replacement.

Recognizing the importance of both the torque-angle and torque-velocity relations, three-dimensional (3D) human strength capabilities (i.e., peak torque as a function of both joint angle and movement velocity) have been increasingly reported. It is not clear, however, the degree to which these surfaces vary between joints, particularly between joints with similar biomechanical configurations. Thus, our goal was to compare 3D strength surfaces between the muscles about the elbow and knee hinge joints in men and women. Peak isometric and isokinetic strength was assessed in 54 participants (30 men) using the Biodex System 3 isokinetic dynamometer. Normalized peak torque surfaces varied significantly between flexion and extension (within each joint) and between joints; however, the normalized 3D torque surfaces did not differ between men and women. These findings suggest the underlying joint biomechanics are the primary influences on these strength surface profiles. Therefore, in applications such as digital human modeling, torque-velocity-angle relationships for each joint and torque direction must be uniquely represented to most accurately estimate human strength capability.

ObjectiveHamstring coactivation during quadriceps activation is necessary to counteract the quadriceps pull on the tibia, but coactivation can be elevated with symptomatic knee osteoarthritis (OA). To guide rehabilitation to attenuate risk for mobility limitations and falls, this study evaluated whether higher antagonistic open kinetic chain hamstring coactivation is associated with knee joint buckling (sudden loss of support) and shifting (a sensation that the knee might give way).DesignAt baseline, median hamstring coactivation was assessed during maximal isokinetic knee extensor strength testing and at baseline and 24-month follow-up, knee buckling and shifting was self-reported. Associations between tertiles of co-activation and knee (1) buckling, (2) shifting and (3) either buckling or shifting were assessed using logistic regression, adjusted for age, sex, knee OA and pain.Results1826 participants (1089 women) were included. Mean±SD age was 61.7±7.7 years, BMI was 30.3±5.5kg/m(2) and 38.2% of knees had OA. There were no consistent statistically significant associations between hamstring coactivation and ipsilateral prevalent or incident buckling or the combination of buckling and shifting. The odds ratios for incident shifting in the highest in comparison with the lowest tertile of coactivation had similar magnitudes in the combined and medial hamstrings, but only reached statistical significance for lateral hamstring coactivation, OR(95%CI) 1.53 (0.99, 2.36).ConclusionsHamstring coactivation during an open kinetic chain quadriceps exercise was not consistently associated with prevalent or incident self-reported knee buckling or shifting in older adults with or at risk for knee OA.

Functional neuroimaging investigations of pain have discovered a reliable pattern of activation within limbic regions of a putative "pain matrix" that has been theorized to reflect the affective dimension of pain. To test this theory, we evaluated the experience of pain in a rare neurological patient with extensive bilateral lesions encompassing core limbic structures of the pain matrix, including the insula, anterior cingulate, and amygdala. Despite widespread damage to these regions, the patient's expression and experience of pain was intact, and at times excessive in nature. This finding was consistent across multiple pain measures including self-report, facial expression, vocalization, withdrawal reaction, and autonomic response. These results challenge the notion of a "pain matrix" and provide direct evidence that the insula, anterior cingulate, and amygdala are not necessary for feeling the suffering inherent to pain. The patient's heightened degree of pain affect further suggests that these regions may be more important for the regulation of pain rather than providing the decisive substrate for pain's conscious experience.